Filter sector

ABSTRACT

A filter sector for a filter disk of a rotating filter, including folded or currugated means having ridges and valleys extending in a longitudinal direction of said means to form filtrate channels, and a filtering medium covering said means. Said means includes at least two elements (9, 10), each having parallel riges (12, 11&#39;) and valleys (11, 12&#39;) and said at least two elements are located in an at least partly overlapping relationship, such that filtrate channels (13) of one element (9) intersect with filtrate channels (14) of the other element (10). Preferably, the filter sector includes two at least substantially equally shaped elements and said elements are disposed such that there is communication between filtrate channels (13, 14) of said elements (9, 10) in zones of said partly overlapping relationship.

The present invention concerns a filter sector for a rotating filterdisk in a rotating filter for filtering relatively solid particles froma slurry or a liquid suspension, such as paper pulp. A plurality of suchfilter sectors, each having the general shape of a truncated sector of acircle, are mounted on a rotatable shaft to form a filter disk, and,generally, a plurality of such filter disks are mounted one after theother on the shaft. The shaft is rotatably supported such that thefilter disks are partially submerged in a liquid to be filtered. Uponrotation of the shaft the filter sectors are consecutively submerged inthe liquid to perform filtering through a filtering medium carried byeach sector and are subsequently raised above the liquid level toperform drying and removal of solids deposited on the filtering medium.The shaft includes channel means for discharging filtrate received fromeach of the filter sectors.

More particularly, the present invention concerns a filter sectorincluding folded or corrugated means defining between ridges of adjacentfolds or corrugations a plurality of channels extending substantially inthe radial direction of the filter sector between a radially outerperiphery thereof and a radially inner periphery thereof. A filter clothor other suitable filtering medium is mounted around the folded orcorrugated means to be supported by the ridges thereof. Filtering takesplace through the filtering medium from both sides of the filter sectorsuch that filtrate enters the substantially radially extending channelsand is discharged through the radially inner end of the filter sector. Afilter sector of this general kind, including but one folded orcorrugated means, is described in SE-B-830069-3 corresponding to U.S.Pat. No. 4,655,920.

This known filter sector suffers from some major drawbacks. Since thefolded or corrugated means generally comprises a metal plate, usually ofacidproof steel, practically insuperable difficulties are encounteredwhen it comes to folding, particularly since the folds or corrugationsare to be located in a fan-like pattern and the filtrate dischargechannels formed by the ridges and valleys are to have a graduallyincreasing height and a gradually increasing cross-section towards theoutlet end of the filter sector. Further, filtrate running along thechannels is continuously contacting the filtering medium and solidsdeposited thereon (and possibly partially protruding therethrough)resulting in a considerable loss of flow rate as well as a risk ofre-wetting the solids.

Consequently, an object of the present invention is to provide a filtersector of the kind stated, which lends itself to a less troublesome andless expensive manufacture while still being more rigid and stable thanexisting filter sectors. Another object of the present invention is toprovide a filter sector of the kind stated, wherein at least asubstantial part of the filtrate is not in contact with the filteringmedium during a substantial part of its flow towards the discharge endof the sector. Still another object of the invention is to provide afilter of the kind stated, which enables a higher dry content of thesolids deposited on the filtering medium. A further object of thepresent invention is to provide a filter sector of the kind stated,which enables a high filtering capacity due to a large exposed area overthe entire filter sector surface.

These and other objects are accomplished by a filter sector of the kindstated having the characteristic features stated in the appended claims.

In one embodiment of the present invention a filter sector includesthree sector parts for receiving and discharging filtrate, viz., afirst, a second and a third sector part.

The major portions of the first and the second sector parts are locatedradially outwards towards the outer periphery of the filter sector andcircumferentially on either sides of the third sector part, and aredenominated "outer sector parts", whereas the major portion of the thirdsector part is located radially inwards towards the discharge, or,radially inner end of the filter sector and between the first and secondsector parts and is denominated "middle sector part". The filtratechannels of the outer sector parts intersect in the middle sector part.

In a preferred embodiment of the present invention there iscommunication between the intersecting channels in the middle part suchthat filtrate flowing along a channel of either of the first part andthe second part of the outer sector parts can "chose" to switch to achannel of the other one of the outer sector parts, or, to remain in itsoriginal channel. In other words, the middle sector part is able toreceive and discharge filtrate from both of the outer sector parts.

In an embodiment particularly advantageous from a productionalviewpoint, the filter sector of the present invention is composed of twosimilarly shaped elements. Preferably, these elements have substantiallythe shape of parallelograms. The elements are so arranged that theysubstantially abut each other at the radially outer andcircumferentially wider end of the filter sector, whereas they at leastalmost entirely overlap each other at the radially inner end of thefilter sector. Hereby the three sector parts obtain the shapes ofsubstantially equal isosceles triangles, the triangles of the outersector parts having their apicis and the triangle of the middle sectorhaving its base facing the radially inner end of the filter sector. Froma viewpoint of structural strength this, in turn, brings about theadvantage that the filter sector has the thickness of two elements alongsubstantially its entire radially inner end where it is attached to theshaft and where the stresses are the greatest.

Alternatively, the filter sector can be manufactured in one piece,particularly if it is manufactured from a plastics material.

In a further preferred embodiment of the invention the connectionbetween the intersecting filtrate channels includes, apart from thechannels of one outer sector part leading into the middle sector part,holes in the channels of the other outer sector part at the transitionfrom one outer sector part to the middle sector part.

In a still further embodiment of the invention a plate shaped element islocated between the intersecting filtrate channels to provide furtherstability and to prevent re-wetting of the filtering medium and solidsdeposited thereon.

The present invention will now be described with reference to theaccompanying schematic drawing, wherein:

FIG. 1 shows one side of a filter sector according to a preferredembodiment of the invention;

FIG. 2 shows a section taken along line II--II of FIG. 1;

FIG. 3 shows a section taken along line III--III of FIG. 1;

FIG. 4 shows a section taken along line IV--IV of FIG. 1; and

FIG. 5 shows at an enlarged scale a part section corresponding to FIG. 4of an alternative embodiment of the invention.

With particular reference now to FIG. 1 there is shown a filter sector 1according to the present invention. As a common in the art of rotatingfilters, the filter sector 1 has the general shape of a sector of acircle having its apex cut off to form a truncated sector of a circle.The filter sector 1 has a radially inner end 2, a radially outer end 3and two substantially radially extending edges 4 and 5. In its radiallyinner end 2 the filter sector 1 has a connecting means 6 for itsattachment to a non-shown rotatable shaft. The connecting means 6includes a collecting means 7 adapted to collect filtrate received fromthe filter sector, and an outlet portion 8 adapted to receive filtratefrom the collecting means, to lead filtrate into the shaft, and, toattach the filter sector to the shaft.

In the preferred embodiment of the present invention shown in FIGS. 1-4,the filter sector 1 includes two plates 9 and 10. The plates 9 and 10are folded, corrugated, or, ondulated so as to define a plurality ofparallel valleys 11 and ridges 12 on one side of each plate 9 and 10,and corresponding ridges 11' and valleys 12', respectively, on theopposite side of each plate, only the valleys being shown in FIG. 1. Theplates 9 and 10 are shaped as substantially equal parallelograms and areplaced in a partly overlapping relationship so that plate 9 is inclinedto the left and plate 10 to the right according to FIG. 1. The partlyoverlapping relationship is such, that the plates 9 and 10 do not atall, or, to only a slight extent, overlap each other in the radiallyouter end 3 of the filter sector (FIG. 2), whereas the extent ofoverlapping gradually increases towards the radially inner end 2 of thefilter sector (FIG. 3) to be complete, or, substantially complete at theradially inner end 2 (FIG. 4). By means of this arrangement, the desiredtruncated sector shape is achieved, and, the filter sector is givensubstantially radially directed filtrate channels 13 and 14corresponding to the valleys 11 and 12', respectively.

To complete the filter sector, its substantially radially extendingedges 4 and 5 are limited by ribs 15 and 16, respectively, having asubstantially U-shaped channelled cross-section, and its radially outerend 3 is limited by an arcuately shaped rib 17 likewise having asubstantially U-shaped channelled cross-section, the respective edgesand radially outer ends of the plates 9 and 10 being introduced into thechannels of the respective ribs. Further, the radially inner overlappingends of the plates 9 and 10 are introduced into the collecting means 7,and a filtering medium, such as a filter cloth 18, for the sake ofclarity shown only in FIGS. 2-4, is arranged around the plates 9 and 10and their limiting ribs 15, 16 and 17.

Further, as a result of the arrangement of the plates 9 and 10 describedabove, the filter sector is divided into three substantially equallyshaped parts, viz., two outer sector parts A and B, where there is justone plate layer, and one middle sector part C, where there are two platelayers due to the overlapping relationship between the plates existingin that area, and the filtrate channels 13 and 14 of the plates 9 and 10intersect in the overlapping area, or, middle sector part C.

Now, regarding the side of the filter sector 1 shown in FIG. 1, it isevident that filtrate entering the filtrate channels 13 of plate 9 flowsalong these channels to be received in collecting means 7, and thatfiltrate entering the filtrate channels 14 of plate 10 flows along thesechannels also to be received in collecting means 7. However, dependingon which one of channels 13 of plate 9 is regarded, filtrate flowingalong channels 13 in filter sector part A is in contact with the filtercloth 18 during a longer or shorter part of the flow due to the factthat channels 13 towards edge 4 enter filter sector part C, i.e., underplate 10, later than channels towards the opposite edge of plate 9. Assoon as filtrate flowing in channels 13 enters under plate 10 (intofilter sector part C), it looses contact with the filter cloth 18 and,as a result, flow resistance is diminished. Also in filter sector partC, where channels 13 intersect with channels 11 of plate 10 facingdownwards in FIG. 1, filtrate is free to "chose" to continue to flow inchannels 13 or to switch over to any of channels 11, depending on whereflow resistance is the lowest.

Evidently, in FIG. 1, the exposed area of plate 9, i.e., filter sectorpart A, is about one third of the entire exposed area of the filtersector 1, whereas the exposed area of plate 10 (filter sector parts Band C) is about two thirds of the entire exposed area. Consequently,plate 10 (parts B and C) receives double the amount of filtrate ascompared to the amount received by plate 9 (part A). Also, filtrateflowing along channels 14 of plate 10 is in constant contact with thefilter cloth 18.

In order to accomplish a more even distribution of filtrate, apertures19 are provided in plate 10, preferably immediately after the transitionbetween sector parts B and C. The apertures 19 are preferably arrangedat the bottoms of the channels 14, or, valleys 12', which preferably arelocated over the innermost channel 13, or, valley 11 of plate 9. By thismeasure, at least a substantial part of the flow along channels 14 isintroduced into the space between plates 9 and 10, i.e., into thechannel 13 mentioned, from which it, again, may "chose" to switch overto a channel 13 on the back side of plate 10, and, possibly, back to achannel 13 of plate 9, depending on where the flow resistance is thelowest.

It is evident that the conditions mentioned are the same on the side ofthe filter sector unexposed in FIG. 1.

In certain applications of the present invention it may be useful tointroduce a plate-shaped element 20 between the plates 9 and 10 in theoverlapping area, i.e., within filter sector part C. Such plate-shapedelement contributes to the structural stiffness of the filter sector andeliminates a possible backwash problem which could arise in certainrotational positions of the filter sector where filtrate flowing in adownward direction between plates 9 and 10 towards collecting means 7could tend to escape through an aperture 19 located at a lower level andthereby re-wet the filtrate cloth 19 and solids deposited thereon.

In the embodiments of the present invention described and shown, thefilter sector includes two separate elements 9 and 10. It may, however,also be possible to manufacture the filter sector in one piece,particularly if it is manufactured from a plastics material.

It may also be possible and suitable to compose the filter sector ofmore than the two elements 9 and 10.

I claim:
 1. A filter sector for a filter disk of a rotating filter,including folded or corrugated means having ridges and valleys extendingin a longitudinal direction of said means to form filtrate channels, anda filtering medium covering said means, wherein said means includes atleast two elements (9, 10), each having parallel ridges (12, 11') andvalleys (11, 12'), and that said at least two elements are located in anat least partly overlapping relationship, such that filtrate channels(13) of one element (9) intersect with filtrate channels (14) of theother element (10).
 2. A filter sector according to claim 1, whereinsaid means includes two elements, (9, 10) being at least substantiallyequally shaped.
 3. A filter sector according to claim 1, said elementsare disposed such that there is communication between filtrate channels(13, 14) of said elements (9, 10) in zones of said partly overlappingrelationship.
 4. A filter sector according to claim 2 having the generalshape of a sector of a circle with a radially outer end and a radiallyinner end, said elements (9, 10) substantially abut each other atwherein said radially outer end and at least approximately entirelyoverlap each other at said radially inner end.
 5. A filter sectoraccording to claim 2, wherein each of said elements substantially hasthe shape of a parallelogram.
 6. A filter sector according to claim 3,wherein said communication exists between sides of said elements facingeach other in zones of said partly overlapping relationship.
 7. A filtersector according to claim 3, wherein apertures (19) are provided in saidelements (9, 10), said apertures being adapted to lead filtrate flowingalong filtrate channels on exposed sides of said elements into filtratechannels on non-exposed sides of said elements within said zones of saidpartly overlapping relationship.
 8. A filter sector according to claim7, wherein said apertures (19) are provided in said zones of overlappingrelationship adjacent the transition between non-overlapping zones ofsaid elements and said zones of overlapping relationship.
 9. A filtersector according to claim 1, wherein a plate shaped element (20) islocated between said elements (9, 10) within zones of said overlappingrelationship.
 10. A filter sector according to claim 1, wherein saidfolded or corrugated means is manufactured in one piece.
 11. A filtersector according to claim 2, wherein said two elements are disposed soas to form a truncated sector of a circle, said sector of a circle beingcomposed of three imaginary, substantially equally shaped figures shapedsubstantially as isoceles triangles, a first and a second of saidtriangles having their apices facing an outlet end of said filtersector, and a third of said triangles having its base facing said outletend and being located between said first and said second triangles.